We will study risk behaviors of human immunodeficiency virus (HIV) infection among homeless mentally ill men in a New York City men's shelter. This is a population at very high risk to contract and transmit HIV infection; we estimate that HIV seroprevalence is in the range of 15-25%. It is also a population accessible to interventions that might change behaviors. One hundred and fifty men enrolled in an on-site psychiatry program in a 1,000 bed men's shelter in New York City will be assessed in two condiitons; first in the shelter, and then 3 months after placement in community housing. Standardized interviews will be administered to assess sexual behaviors, drug use, and knowledge and attitudes relevant to behavior change, at these two time points. These will be supplemented by ethnographic observations. Thus, the study will gather a rich array of descriptive data on risky behaviors in this marginal subculture. In addition, we will test hypotheses on high risk sexual behaviors in these men that have implications for intervention against HIV. These hypotheses include: 1. Strong predictors of high risk sexual behaviors in this population include age under 30 years, crack cocaine use, cognitive impairment, and a childhood history of out-of-home placement or running away. 2. The nature and frequency of unprotected sexual activities of homeless mentally ill men vary markedly between shelter and community settings. As these men move from the shelter into the community, the tend to have less sex with men, more sex with women, and a broader range of sexual partners. 3. Homeless mentally ill men generally have accurate knowledge about the main paths of HIV transmission and can assess personal result in minimization of sexual risk behaviors among sexually active men in this population. The continuation of high risk behaviors in men who understand the risks involved is related to poor self-efficacy. Findings will be used to contribute to the design of preventive interventions.